Process for producing malleable iron castings



Patented Feb. 11, 1941 PATENT OFFICE PROCESS FOR- PRODUCING IRONCASTINGS Gerth Herrmann, Wnppertal-Barmen, Germany No Drawing.Application February 28, 1939, Se-

rial No. 259,027. In Germany January 18,

2 Claims. (Cl. 148-16) Thisinvention is concerned with a new method forproducing malleable iron castings.

The usual method for obtaining white heart malleable iron castingsconsists in placing the raw castings together with comminuted iron orein layers into annealing pots, so-called temper pots, and subjectingthem in a suitable oven or furnace for a considerable time to atemperature of about 1000 C. The carbon which is chemically bound withiron is thereby partly liberated in the form of free carbon (tempercarbon), depending on the annealing time and the temperature employed.Part of this liberated carbon is wholly withdrawn from the casting andescapes in gaseous form, being chemically bound as carbon monoxide andcarbon dioxide by the oxygen liberated from the iron ore. One of thedisadvantages of this method resides in th ne'- cessity of heating up toand maintaining at the annealing temperature not only the castings beingtreated but also the annealing pots and the iron ore, which constitute amultiple of the mass and weight of the castings, thereby occasioning aconsiderable and quite costly consumption of heat.

The present invention avoids the drawbacks of the usual method byaccomplishing the annealing and decarbonizing of the material accordingto a new process which uses a uniform gaseousatmosphere and dispenseswith the use of auxiliary means, such as annealing pots and iron ore andthe like. The details pertaining to the new process are explained below.

The new process is based on the discovery, supported and tested byexperiments and practical use, that satisfactory and unobjectionableresults in effective decarbonization are obtained by heating orannealing the castings in a suitably heated retort in an atmosphere ofilluminating gas, or gas of similar composition, for example, generatorgas, water gas, Mond gas, or the like. The castings are for this purposepacked in lightweight iron loading baskets and are introduced preferablyunder a seal-protected hood into an annealing oven which may be heatedelectrically, by gas or by coal, or in any other.

either partially or wholly, in order to form carbon dioxide, which istheactive ingredient for oxidation of the carbon liberated from thecastings. However, according to the preferred form of the invention,ordinary unburned gas is used, but 5 is mixed with a small amount of airbefore or as it is introduced into the annealing chamber. The oxygen ofthe air produces a partial combustion of the gas (without flameformation), reacting with carbon monoxide which is a constit- 10 uent ofall the gases suggested for use to form carbon dioxide, and therebyobtain a gas suitable for the desired reaction.

' In order to avoid a cessation of the chemical reaction and to obtainsufficient decarbonization 15 of the casting material, the gas whichabsorbs thecarbon must be continuously removed and renewed by fresh gas,together with the requisite small quantity of air. The gas which iswithdrawn from the oven still has a high heating 20 value and may beused for any desired and suitable heating purposes, thus rendering themethod very economical.

Depending on the condition of the gas employed for the process, it maybedesirable to 25 withdraw its moisture content, which otherwise couldcause spunk or scale formation on the'surface of the iron. A suflicientdrying of the gas may be obtained, for example, by conducting itthrough'calcium chloride or through silica jel, or by subjecting it tocooling. Such separate removal of moisture is, however, usuallyunnecessary in practice, since small traces of moisture cannot actdetrimentally.

An example of carrying out the new process is described below withrespect to a raw casting having a low carbon content of about 2.8% to3.1%, a silicon content of 0.9% to 1.1%, a manganese content of about0.35%, and a sulphur content of about-0.2%., 40

The casting is placed in a retort, heated to 980 C., and annealed bysubstantially maintaining that temperature for about 24 hours. At theconclusion of this first annealing period, the closure, for example, thesealhrg hood, of the retort or oven, is removed in order to obtain acooling of the casting in air down to about 760 C. This lattertemperature is maintained for about 10 hours, with subsequentprogressive slow cooling amounting to an hourly reduction of tem--perature by about 5 C., down to 650 C., whereupon the casting isremoved from the retort. A gas mixture comprising substantially equalparts of air and illuminating gas is introduced into the retort andcontinuously circulated through it during the pre-heating and alsoduring the annealing period. For example, in the annealing of about 4tons of raw castings a total amount of about 200 cubic meters of amixture of gas and air in the ratio of 1:1 is conducted through theretort during the entire annealing operation. No appreciable gas supplyis required during the latter part of the process, that is, during thecooling from substantially 760 C. to 650 C.

It is understood that the terms used here and also in the accompanyingclaims are to be interpreted with sensible latitude. Reference to aspecific gas, wherever used, is intended to comprehend the use of anequivalent gas or gas mixture to the extent noted in the foregoingspecification. Likewise, references to specific temperature conditionsare meant to convey temperatures of or substantially in the neighborhoodof those indicated.

Changes may be made within the scope and spirit of the appended claims,wherein is defined what is believed to be new and desired to haveprotected by Letters Patent of the United States.

What is claimed is:

1. The process of producing white heart malleable iron castings, whichconsists in placing the raw casting into a sealed retort, heating saidretort to heat the casting contained therein to annealing temperaure,and maintaining in said retort during the entire process of heating andannealing oi said casting a gaseous atmosphere consisting ofilluminating gas mixed with air in such proportion that only crackingthereof, that is, a chemical reaction without flame formation takesplace to obtain effective decarbonization of said casting withoutoxidation and formation of scale thereon.

2. The process defined in claim 1, together with the step ofcontinuously circulating through said retort a fresh gaseous mixture ofthe composition specified and maintaining the pressure of said gaseousmixture substantially uniform, 20

